True, but it works this way. And, version 1.4 makes the Content-Length header mandatory. I actually did it that way in my QP spamassassin plugin. The downside though is that to properly calculate Content-Length, I had to convert the internal representation of the message to it's SMTP format (headers + delim + body) to get the correct Content-Length.  I didn't test with Haraka to verify this is still the case but my guess is that it is. That's a waste of CPU and RAM when just saying 1.3 works well and is very, very unlikely to run into problems in real world cases.